Magnetic inhomogeneity in colossal magnetoresistive La0.67Ca0.33MnO3-delta perovskite ceramics

Abstract

Magnetic inhomogeneity in colossal magnetoresitive lanthanum manganites and its effect on MR properties are reported. Polycrystalline bulk specimens of La0.67Ca0.33MnO3 were prepared by solid state reaction and sol-gel route. By controlling materials processing parameters, CMR specimens with different magnetic quality (M-0 = 91-93 emu g(-1), T-c = 240-270 K) were obtained. The MR properties of these specimens were characterized to be a broad, rather than a sharp as in a typical CMR materials, transition of semiconductor to metal and multiple peaks in MR versus T curve, which was explained by the co-existence of several La1-xCaxMnO3 phases with different magnetic transition temperature (T-c). The extent of inhomogeneity was in coincidence with the magnetic quality of the specimens. The magnetic inhomogeneity was found to severely degrade a field sensitivity at the temperature where the peak MR ratio was observed. The presence of paramagnetic secondary phase at the temperature was proposed to explain the degradation of field sensitivity. (C) 1998 Elsevier Science B.V. All rights reserved.